TWO-STAGE CATALYST FOR REMOVAL OF NOx FROM EXHAUST GAS STREAM

ABSTRACT

A co-catalyst system for the removal of NO x  from an exhaust gas stream has a layered oxide and a spinel of formula Ni 0.15 Co 0.85 CoAlO 4 . The system converts to nitric oxide to nitrogen gas with high product specificity. The layered oxide is configured to convert NO x  in the exhaust gas stream to an N 2 O intermediate, and the spinel is configured to convert the N 2 O intermediate to N 2 .

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of application Ser.No. 15/476,374, filed Mar. 31, 2017, which is herein incorporated byreference in its entirety.

TECHNICAL FIELD

The present disclosure generally relates to catalysts for treatment ofan exhaust gas stream and, more particularly, to two-stage catalysts forremoval of nitrogen oxides from an exhaust gas stream generated by aninternal combustion engine.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it may be described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presenttechnology.

Catalysts effective at removing NO_(x) from exhaust emissions aredesirable, in order to protect the environment and to comport withregulations directed to that purpose. It is preferable that suchcatalysts convert NO_(x) to inert nitrogen gas, instead of convertingNO_(x) to other nitrogen-containing compounds. Catalysts that areeffective at low temperature may have additional utility.

Accordingly, it would be desirable to provide a catalyst for the removalof NO_(x) from exhaust gas, that is effective at low temperature andthat has high N₂ product specificity.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In various aspects, the present teachings provide a catalytic converterfor the removal of NO_(x) from an exhaust gas stream. The catalyticconverter includes an inlet configured to receive the exhaust gas streaminto an enclosure; and an outlet configured to allow the exhaust gasstream to exit the enclosure. The catalytic converter further includes aco-catalyst system contained inside the enclosure. The co-catalystsystem includes a layered oxide configured for catalyzing a reductionreaction of at least one of NO and NO₂ to generate N₂O. The co-catalystsystem also includes a spinel having a formula, Ni_(y)Co_(1-y)CoAlO₄,wherein y is a value within a range of about 0.1 to about 0.9,inclusive, for catalyzing a decomposition reaction of N₂O to N₂.

In other aspects, the present teachings provide a two-stage method forthe removal of NO_(x) from an exhaust gas stream. The method includes astep of flowing the exhaust gas stream through a co-catalyst system. Theflowing step includes exposing the exhaust gas stream to a layered oxideand catalyzing a reduction of at least one of NO and NO₂ to generateN₂O. The flowing step also includes exposing the exhaust gas stream to aspinel having a formula Ni_(0.15)Co_(0.85)CoAlO₄ to decompose the N₂O toN₂.

In still other aspects, the present teachings provide a catalyticconverter for the removal of NO_(x) from an exhaust gas stream. Thecatalytic converter includes an inlet configured to receive the exhaustgas stream into an enclosure; and an outlet configured to allow theexhaust gas stream to exit the enclosure. The catalytic converterfurther includes a co-catalyst system contained inside the enclosure.The co-catalyst system includes a layered oxide configured forcatalyzing a reduction reaction of at least one of NO and NO₂ togenerate N₂O. The layered oxide has a formula, La_(2-x)M_(x)QO₄,wherein: M is a cationic metal selected from the group consisting of:Ca, Sr, Ba, and a combination thereof; Q is a cationic metal selectedfrom the group consisting of: Fe, Ni, Co, and a combination thereof; andx is within a range of from about 0.01 to about 1.5, inclusive. Theco-catalyst system also includes a spinel having a formula,Ni_(y)Co_(1-y)CoAlO₄, wherein y is a value within a range of about 0.1to about 0.9, inclusive, for catalyzing a decomposition reaction of N₂Oto N₂.

Further areas of applicability and various methods of enhancing theabove coupling technology will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present teachings will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1A is a side schematic view of a variation of a co-catalyst systemof the present disclosure;

FIG. 1B is a side schematic view of another variation of the co-catalystsystem;

FIG. 2A is a Co2p_(3/2) x-ray photoelectron spectroscopy (XPS) spectrumof a LaBaCoO₄ layered oxide;

FIG. 2B is a Fe2p_(3/2) XPS of a FeBaCoO₄ layered oxide;

FIG. 3A is an x-ray diffraction (XRD) pattern of the layered oxide ofFIG. 2A;

FIG. 3B is an XRD pattern of the layered oxide of FIG. 2B;

FIG. 3C is an XRD pattern of Ni_(0.15)Co_(0.85)CoAlO₄ spinel;

FIG. 4A is a plot of NO conversion percentage as a function oftemperature for LaBaCoO₄;

FIG. 4B is a plot of NO conversion percentage as a function oftemperature for LaBaFeO₄;

FIG. 4C is a plot of NO conversion percentage as a function oftemperature for Ni_(0.15)Co_(0.85)CoAlO₄;

FIG. 4D is a plot of NO conversion percentage as a function oftemperature for a co-catalyst system havingLaBaCoO₄+Ni_(0.15)Co_(0.85)CoAlO₄;

FIG. 4E is a plot of NO conversion percentage as a function oftemperature for a co-catalyst system havingLaBaFeO₄+Ni_(0.15)Co_(0.85)CoAlO₄;

FIGS. 5A and 5B plot production of N₂ and percentage of NO reduced toN₂, respectively, by various catalyst compositions; and

FIGS. 6A and 6B are plots of N₂ production and percentage of decomposedNO converted to N₂, respectively, for various alternative co-catalystconfigurations.

It should be noted that the figures set forth herein are intended toexemplify the general characteristics of the methods, algorithms, anddevices among those of the present technology, for the purpose of thedescription of certain aspects. These figures may not precisely reflectthe characteristics of any given aspect, and are not necessarilyintended to define or limit specific embodiments within the scope ofthis technology. Further, certain aspects may incorporate features froma combination of figures.

DETAILED DESCRIPTION

The present teachings provide two-stage catalysts for the removal ofnitrogen oxides (NO_(x)) from an exhaust gas stream. The presentlydisclosed two-stage catalysts employ a two-step chemical transformationto decompose NO_(x) to nitrogen and oxygen gas, even at relatively lowtemperature.

The presently disclosed two-stage catalysts include a layered oxide, forthe decomposition of NO_(x) to N₂O, and a spinel component, for thedecomposition of the N₂O intermediate to N₂ and O₂. Data describedherein show that layered oxides are most effective at decomposing NOinto N₂O, not N₂. N₂O is known for being a major greenhouse gas andpowerful pollutant. This characteristic of N₂O formation makes layeredoxides a problematic and non-obvious NO catalytic material, especiallyat lower temperatures ≤550° C. where layered oxides are not particularlyactive at N₂ production to offset this N₂O formation. Therefore, thedesign of a co-catalyst that purposely uses the layered oxide N₂Oformation to provide a functional advantage is needed. The coupling ofthe layered oxide with a spinel of overlapping temperature rangeactivity for N₂O decomposition, as described below, allows for the N₂Ogenerated to be further decomposed to N₂. Overall, the decomposition ofNO to N₂ is approximately doubled using the co-catalyst design comparedto either of the constituent catalysts individually.

Thus, and with reference to FIGS. 1A and 1B, a co-catalyst system 100for the decomposition of NO_(x) is disclosed. The co-catalyst system 100includes a layered oxide 110. In some implementations, the layered oxidecan include layered oxide nanoparticles. In certain implementations, thelayered oxide 110 can have a formula according to Formula A:

La_(2-x)M_(x)QO₄  A.

where M is a cation of at least one Group II metal; Q is a cation ofiron, cobalt, nickel, or a combination thereof; and x is a value withina range of about 0.1 to about 1.5, inclusive. In some implementations, Mcan be a cation of strontium, barium, calcium, or a combination thereof.In certain implementations, the layered oxide can be a layeredperovskite oxide, wherein lanthanum and M include divalent cations, andQ includes tetravalent cations.

In some implementations, the layered oxide 110 can be at least one ofLaBaCoO₄ and LaBaFeO₄. As will be described further below, the layeredoxide will be configured to decompose NO_(x) substantially to N₂O.Without implying limitation, such decomposition catalyzed by the layeredoxide 110 can proceed, for example, through reactions such as shownbelow in Reactions I and II:

4 NO₂→2N₂O+3O₂  (I)

4 NO→2N₂O+O₂  (II)

The co-catalyst further includes a spinel 120. In certain variations,the spinel 120 can have a formula, Ni_(y)Co_(1-y)CoAlO₄, wherein y is avalue within a range of about 0.1 to about 0.9, inclusive. In certainspecific implementations, the spinel 120 can beNi_(0.15)Co_(0.85)CoAlO₄. As will be described further below, the spinel120 will be configured to decompose N₂O to N₂ and O₂. Without implyinglimitation, such decomposition catalyzed by the spinel 120 can proceed,for example, through reactions such as shown below in Reaction III:

2 N₂O→2N₂+O₂  (III)

It will thus be appreciated that, in operation of the co-catalyst system100, the layered oxide 110 operates, in part, to partially decomposeNO_(x) and produce an intermediate species, N₂O. The spinel 120 thenoperates to further decompose the intermediate species, N₂O, to thedesired products, N₂ and O₂.

In some implementations, the layered oxide 110 and the spinel 120 can bespatially separated from one another, as illustrated in the example ofFIG. 1A. In such implementations, the layered oxide and spinel 110, 120can be in adjacent contact, or, as shown in FIG. 1A, can be separated bya separation space 130. When present, such a separation space can besubstantially vacant, or can be occupied with a porous, gas permeable,or other suitable material.

A co-catalyst system 100 of the present disclosure can be deployed in anenclosure 140 having an inlet and an outlet. The enclosure 140 can beconfigured to receive an exhaust gas stream through the inlet and toexit the exhaust gas stream through the outlet, such that the exhaustgas stream has a flow direction (represented by the arrow F in FIGS. 1Aand 1B). In implementations in which the layered oxide 110 and spinel120 are spatially separated (FIG. 1A), the layered oxide 110 can bepositioned in an upstream portion of the exhaust gas stream and thespinel 120 can be positioned in a downstream portion of the exhaust gasstream. As used herein, the expression “upstream portion” can refer to aregion proximal to a gas inlet portion; and the expression “downstreamportion” can refer to a region proximal to a gas outlet portion.

It will be understood that in implementations in which the layered oxide110 is positioned in an upstream portion of the exhaust gas stream andthe spinel 120 is positioned in a downstream portion of the exhaust gasstream, this can cause the exhaust gas stream to encounter the layeredoxide 110 before the exhaust gas stream encounters the spinel 120. Thus,in such implementations, as the exhaust gas stream flows through theco-catalyst system 100, it first encounters the layered oxide 110 sothat NO_(x) within the exhaust gas stream is substantially or entirelydecomposed to N₂O in consequence.

In other implementations, the layered oxide and spinel 110, 120 can beintermixed, substantially occupying the same space, as shown in FIG. 1B.In such implementations, the layered oxide and spinel 110, 120 occupyoverlapping regions such that NO_(x) are converted to N₂O, and N₂O isconverted to N₂ and O₂, within overlapping regions. It will beunderstood that various intermediate positions can also be employed,such as partial overlap, stepped or gradual concentration gradients,etc. In general, it is desirable that all portions of the layered oxide110 be positioned upstream of at least some portion of the spinel 120. Aco-catalyst system 100 of the present disclosure in which the layeredoxide 110 is upstream and the spinel 120 is downstream, as shown in FIG.1A, can be referred to alternatively as a “sequential co-catalyst.” Aco-catalyst system 100 in which the layered oxide 110 and the spinel 120are substantially intermixed, as shown in FIG. 1B, can be referred toalternatively as a “mixed co-catalyst”.

FIGS. 2A and 2B show x-ray photoelectron spectroscopy (XPS) data for twoexemplary layered oxides, LaBaCoO₄ and LaBaFeO₄, respectively. Thesurfaces of the LaBaCoO₄ and LaBaFeO₄ exemplary layered oxides 110contain Co³⁺ and Fe³⁺ cations, respectively, based on the XPS bindingenergy differences between the main and satellite peaks shown in FIGS.2A and 2B. Binding energy differences of 11.5 and 7.8 eV at the 2p_(3/2)binding energies are representative of Co³⁺ and Fe³⁺, respectively. Thisis in contrast to the anticipated observation, where binding energydifferences between the main and satellite peaks would be ˜4.8 and ˜5.9eV. These smaller binding energy differences correspond to Co²⁺ and Fe²⁺respectively, and are in line with the assumed 2+ cation B-siteoccupation for layered oxides of the general formula is A₂BO₄. Butbecause defect sites for layered oxides form the 3⁺ version of theB-site and that the exemplary samples are in the form of nanoparticleswith an expected occurrence of surface defects, the B-site 2p_(3/2) XPSspectra showing the presence of 3+ cations is therefore logicallyexplainable.

Powder x-ray diffraction (XRD) patterns for LaBaCoO₄, LaBaFeO₄, andNi_(0.15)Co_(0.85)CoAlO₄ are shown in FIGS. 3A-3C, respectively.Scherrer analysis of the XRD peak broadening for LaBaCoO₄, LaBaFeO₄ andNi_(0.15)Co_(0.85)CoAlO₄ determined crystallite sizes to be 14, 7, and11 nm, respectively, in these examples.

FIGS. 4A-E show nitric oxide (NO) conversion percentages for fivedifferent catalysts exposed to a nitric oxide stream at varyingtemperatures, under conditions described below in the Examples section.The five catalysts of FIGS. 4A-E are: LaBaCoO₄ only (FIG. 4A); LaBaFeO₄only (FIG. 4B); Ni_(0.15)Co_(0.85)CoAlO₄ only (FIG. 4C); a co-catalystsystem 100 having LaBaCoO₄ upstream of Ni_(0.15)Co_(0.85)CoAlO₄ (FIG.4D); and a co-catalyst system 100 having LaBaFeO₄ upstream ofNi_(0.15)Co_(0.85)CoAlO₄ (FIG. 4E). It is to be noted that the totalamount of catalyst present is the same in each of the samplescorresponding to FIGS. 4A-4E.

A comparison of FIG. 4A and FIG. 4B shows that, while LaBaFeO₄ andLaBaCoO₄ have very comparable NO conversion percentages across thetemperature range 350-550° C., LaBaCoO₄ converts about 50% more NO at650° C. This result suggests that LaBaCoO₄ may be particularly suitableas a layered oxide 110. A comparison to the results in FIG. 4C indicatesthat the exemplary spinel 120, by itself, has only half the NOconversion percentage shown by LaBaCoO₄ (FIG. 4A) and 75% of thatrecorded for LaBaFeO₄ (FIG. 4B) at 650° C. However, at lowertemperatures, the spinel 120 exhibits moderately higher NO conversionpercentages than do the layered oxides 110.

The co-catalyst systems 100 of FIGS. 4D and 4E are arrayed as shown inFIG. 1A, with the layered oxide 110 upstream and the spinel 120downstream. It will thus be appreciated that in FIGS. 4D and 4E, thelayered oxide 110 (LaBaCoO₄ or LaBaFeO₄) is encountered first by the NOgas stream, and the spinel 120 (Ni_(0.15)Co_(0.85)CoAlO₄) issubsequently encountered by the gas stream. A comparison of FIGS. 4A-4Eshows that the co-catalysts 100 (FIGS. 4D and 4E) have comparable NOdecomposition percentages to those of the individual components (FIGS.4A-4C) at lower temperatures, with improved NO decomposition percentagesat higher temperatures.

FIG. 5A illustrates plots of N₂ production by the five catalysts ofFIGS. 4A-4E, in the temperature range 350-550° C. It is readily apparentthat the two co-catalyst systems 100 produce N₂ as or more efficientlythan do the layered oxides 110 or the spinel 120 alone, at alltemperatures. The co-catalyst systems 100 produce N₂ more efficientlythan do all of the individual components at 450° C. In particular, thelayered oxides 110 produce virtually no N₂ in the temperature range350-450° C. This demonstrates that the NO that is decomposed by theselayered oxides 100 alone within that temperature range (FIGS. 4A and 4B)is converted to other nitrogen-containing species.

FIG. 5B illustrates plots of the percentage of NO reduced to N₂ for thesame five catalysts, in the temperature range 350-550° C. Statedalternatively, of that portion of NO that is decomposed by a givencatalyst at a given temperature (FIGS. 4A-4E), FIG. 5B plots thepercentage of it that is converted to N₂, as opposed to another species.Stated yet more succinctly, FIG. 5B shows the N₂ specificity of productformation. The results show that both of the co-catalyst systems 100have superior N₂ specificity compared to the layered oxides 110 or thespinel 120 alone at 350-450° C. The co-catalyst system 100 having alayered oxide 110 of LaBaCoO₄, in particular, has superior N₂specificity at all temperatures, with an approximately 6-fold higherspecificity than the spinel 120 alone at the low temperature of 350° C.

The results of FIGS. 4A-4E and FIGS. 5A-5B generally indicate thatdeployment of the layered oxide 110 and the spinel 120 in thearrangement of FIG. 1A results in a synergistic effect, and isconsistent with the concept of a two-stage catalysis operating throughan N₂O intermediate, as discussed above. The results further suggestthat LaBaCoO₄ is a particularly effective layered oxide 110 for use inthe co-catalyst system 100.

FIG. 6A plots N₂ production catalyzed by two mixed co-catalysts and twoinverted co-catalysts. FIG. 6B shows N₂ specificity of product formationfor the same four catalysts. The expression “inverted co-catalyst”refers to a catalyst similar to the co-catalyst system as shown in FIG.1A, but with the positions of layered oxide 110 and spinel 120 reversedrelative to the flow direction, F. Stated alternatively, an invertedco-catalyst is one in which the spinel 120 is upstream and the layeredoxide 110 is downstream.

A comparison of FIGS. 6A-6B to FIGS. 5A-5B indicates that theco-catalyst systems 100 having intermixed layered oxide 110 and spinel120, as in FIG. 1B, are generally less effective than are theco-catalyst systems 100 having layered oxide 110 upstream and spinel 120downstream, as in FIG. 1A. The results further indicate that theinverted co-catalysts are even less effective. This further supports theview that a co-catalyst system 100 of the present disclosure operatesthrough an N₂O intermediate, as discussed above.

Also disclosed is a two-stage method for removal of NO_(x) from anexhaust gas stream. The method for removal of NO_(x) from an exhaust gasstream includes a step of flowing the exhaust gas stream through aco-catalyst system 100. The co-catalyst system 100, as employed in themethod for removal of NO_(x) from an exhaust gas stream, is as describedabove. The flowing step thus includes: (i) exposing the exhaust gasstream to a layered oxide and catalyzing a reduction of at least one ofNO and NO₂ to generate N₂O; and (ii) contacting the exhaust gas streamwith a spinel to decompose the N₂O to N₂. It will be understood that thelayered oxide and the spinel, as used in the method, are the same in allrespects as the layered oxide and spinel as described above. Inparticular, the layered oxide has the formula La_(2-x)M_(x)QO₄, and thespinel has the formula Ni_(y)Co_(1-y)CoAlO₄, as described above. Itshould be understood that the use of different terms “exposing” and“contacting” does not necessarily denote manner of physical interactionbetween the exhaust gas and the layered oxide is different from themanner of physical interaction between the exhaust gas and the spinel.The term “two-stage” as used with respect to the method thus indicatesthat the exhaust gas stream is exposed to two distinct catalysts, thefirst catalyst producing, at least in part, an N₂O intermediate, and thesecond catalyst producing N₂.

In some implementations, exposing the exhaust gas stream to a layeredoxide can partially or completely chronologically precede contacting theexhaust gas stream with the spinel. Thus, in such implementations, theexhaust gas stream will generally encounter the layered oxide prior tothe spinel. In some particular instances of such implementations, theexhaust gas stream can include a step of recirculating the exhaust gasstream through the co-catalyst system 100. Thus, in such particularinstances, the method includes first exposing the exhaust gas stream tothe layered oxide, then contacting the exhaust gas stream with thespinel, then repeating in the same order. For example, an exhaust gasstream produced by a manufacturing facility can be recirculated throughthe co-catalyst system 100 one or more times prior to an eventualrelease or additional processing.

Further disclosed is an apparatus for removal of NO_(x) from an exhaustgas stream. The apparatus includes an enclosure; an inlet, configured toreceive the exhaust gas stream into the enclosure; and an outlet,configured to allow the exhaust to exit the enclosure. The apparatusfurther includes a co-catalyst system 100 inside the enclosure, and thatis as described above. The inlet and outlet of the apparatus cangenerally correspond to the inlet and outlet of FIGS. 1A and/or 1B. Anexample of such an apparatus can be a catalytic converter.

Various aspects of the present disclosure are further illustrated withrespect to the following Examples. It is to be understood that theseExamples are provided to illustrate specific embodiments of the presentdisclosure and should not be construed as limiting the scope of thepresent disclosure in or to any particular aspect.

EXAMPLES

All Example syntheses are conducted under ambient conditions. Allchemicals are used as received. With regard to the layered oxides, themetal salt solutions used throughout all of the syntheses are formedmost efficiently with sonication. Also, using pre-formed metal saltsolutions also dramatically increased the ease of creating reactionemulsions. All emulsions are kept stirring throughout the syntheses soas to avoid any of them breaking. The layered oxide calcinationprocedures conducted are all done in the same manner for all samples,under a flow of argon with a dwell temperature of 400° C. for 6 hours.

Example 1. Formation of NaOH/CTAB Emulsion

A solution of 3.5 g NaOH dissolved in 25 mL H₂O is added to a flask. 23mL n-butanol, 112 mL hexane, 22.5 g cetyltrimethylammonium bromide(CTAB), and a stir bar is then added to this flask. The mixture isstirred vigorously to fully dissolve/disperse all components.

Example 2. Synthesis of LaBaCoO₄

An aqueous solution of 1.734 g La(NO₃)₃.6H₂O, 1.047 g Ba(NO₃)₂ and 0.953g CoCl₂.6H₂O, in 14 mL of H₂O is added to a flask. 23 mL n-butanol, 112mL hexane, 22.5 g CTAB are subsequently added, and the mixture isstirred with a magnetic stir bar. Once all components are dissolved andcombined to form an emulsion, the NaOH/CTAB emulsion is added to thisLaBaCo/CTAB emulsion, with continuing stirring.

After 30 mins of stirring, 200 mL of ethanol is added to cause theproduct to precipitate. The product is collected, washed with ethanolfollowed by H₂O and dried at 180° C. in the air. Calcination isconducted as described above.

Example 3. Synthesis of LaBaFeO₄

A pre-formed aqueous solution of 1.734 g La(NO₃)₃.6H₂O, 1.047 gBa(NO₃)₂, and 0.796 g FeCl₂.4H₂O, in 14 mL of H₂O, is added to a flask.23 mL n-butanol, 112 mL hexane, 22.5 g CTAB are subsequently added, andthe mixture is stirred with a magnetic stir bar. An emulsion is thenallowed to form with aggressive stirring. The NaOH/CTAB emulsion isadded to this LaBaFe/CTAB emulsion, always stirring.

After an additional 30 mins of stirring, precipitation is induced with200 mL of ethanol. The product is collected, washed with ethanolfollowed by H₂O and dried at 180° C. in the air. Calcination isconducted as described above.

Example 4. Synthesis of Ni_(0.15)Co_(0.85)CoAlO₄

Stoichiometric quantities of Co(NO₃)₂, Al(NO₃)₃, and Ni(NO₃)₂ areprepared with a 0.25 M cation concentration, stirred for 30 minutes atroom temperature, then 1.5 molar equivalents of anhydrous citric acid isadded. The solution is heated to 60° C. for two hours with stirring.Afterwards, ethylene glycol is added at a 40/60 molar ratio with respectto citric acid, and the temperature is increased to 90° C. This isstirred until a gel is formed (˜16 hours). The resulting gel is placedin an oven under air, and the temperature is increased to 130° C. at 1°C./min, and maintained for four hours, to promote polyesterification.Next, the temperature is increased to 300° C., linearly at 1° C./min,and held for one hour to decarbonize the sample. The decarbonized sampleis ground thoroughly with an agate mortar and pestle, placed in afurnace, under air, and the temperature is increased to 600° C. at 1°C./min, and held for four hours prior to returning to ambient condition.

Catalytic Testing

NO decomposition performance is evaluated using a fixed bed quartztubular reactor (PID Particulate Systems Microactivity Reference) with 1cm diameter, while flowing 1% NO/He with 1% Ar tracer, over fourseparate catalyst configurations. The configuration corresponding toFIG. 1B (mixed co-catalysts or single component catalysts) is a singlebed, composed of a mixture of approximately 500 mg catalyst diluted with100 mg quartz sand, to yield a bed length of 1 cm while maintaining aGHSV of 2,100 h⁻¹. In the configuration corresponding to FIG. 1Asequential catalysts or inverted catalysts, the samples are divided intotwo separate 1 cm length beds, separated by quartz wool.

Prior to reaction, the catalysts are pretreated in UHP He for 30 minutesat 400° C., and reactions are conducted for two hours each at 350, 450,550, and 650° C., utilizing only the last 10 minutes of data at eachcondition. An online mass spectrometer (MKS Instruments Inc. Cirrus-2)is utilized to calculate NO conversion by linear interpolation betweenthe base line m/z 30 signal (He flow only), and the m/z 30 signal of thereaction mixture through reactor bypass, while monitoring m/z 28, 32,40, 44, 46 (N₂, O₂, Ar, N₂O, NO₂). The Ar present in the reactant streamacted as tracer of constant concentration, and the Ar signal at m/z=40is used to normalize each of the mass spectrum traces. To determine thetotal N₂ production, a calibration gas consisting of 1137 ppm N₂ in a Hebalance is utilized to calibrate the m/z=28 response by creating acalibration curve. The calibration curve is utilized to calculate aquantified N₂ production.

The preceding description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. As usedherein, the phrase at least one of A, B, and C should be construed tomean a logical (A or B or C), using a non-exclusive logical “or.” Itshould be understood that the various steps within a method may beexecuted in different order without altering the principles of thepresent disclosure. Disclosure of ranges includes disclosure of allranges and subdivided ranges within the entire range.

The headings (such as “Background” and “Summary”) and sub-headings usedherein are intended only for general organization of topics within thepresent disclosure, and are not intended to limit the disclosure of thetechnology or any aspect thereof. The recitation of multiple embodimentshaving stated features is not intended to exclude other embodimentshaving additional features, or other embodiments incorporating differentcombinations of the stated features.

As used herein, the terms “comprise” and “include” and their variantsare intended to be non-limiting, such that recitation of items insuccession or a list is not to the exclusion of other like items thatmay also be useful in the devices and methods of this technology.Similarly, the terms “can” and “may” and their variants are intended tobe non-limiting, such that recitation that an embodiment can or maycomprise certain elements or features does not exclude other embodimentsof the present technology that do not contain those elements orfeatures.

The broad teachings of the present disclosure can be implemented in avariety of forms. Therefore, while this disclosure includes particularexamples, the true scope of the disclosure should not be so limitedsince other modifications will become apparent to the skilledpractitioner upon a study of the specification and the following claims.Reference herein to one aspect, or various aspects means that aparticular feature, structure, or characteristic described in connectionwith an embodiment or particular system is included in at least oneembodiment or aspect. The appearances of the phrase “in one aspect” (orvariations thereof) are not necessarily referring to the same aspect orembodiment. It should be also understood that the various method stepsdiscussed herein do not have to be carried out in the same order asdepicted, and not each method step is required in each aspect orembodiment.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations should not beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. A catalytic converter for the removal of NO_(x)from an exhaust gas stream operating between 350 and 550° C., thecatalytic converter comprising: an inlet configured to receive theexhaust gas stream into an enclosure; an outlet configured to allow theexhaust gas stream to exit the enclosure; and a co-catalyst systemcontained inside the enclosure, the co-catalyst system having: a layeredoxide configured for catalyzing a reduction reaction of at least one ofNO and NO₂ to generate N₂O; and a spinel having a formula,Ni_(y)Co_(1-y)CoAlO₄, wherein y is a value within a range of about 0.1to about 0.9, inclusive, for catalyzing a decomposition reaction of N₂Oto N₂.
 2. The catalytic converter according to claim 1, wherein theco-catalyst system is configured as a sequential co-catalyst and theexhaust gas stream moves in a flow direction, with the layered oxidebeing positioned upstream of the spinel structure relative to the flowdirection.
 3. The catalytic converter according to claim 2, wherein theenclosure defines first and second adjacent chambers, wherein the firstchamber comprises the layered oxide and receives the exhaust gas from anupstream portion of the catalytic converter, and the second chambercomprises the spinel structure and receives the exhaust gas afterpassing through the first chamber.
 4. The catalytic converter accordingto claim 3, further comprising a separation space between the firstchamber and the second chamber.
 5. The catalytic converter according toclaim 1, wherein the co-catalyst system is configured as a mixedco-catalyst.
 6. The catalytic converter according to claim 5, whereinthe layered oxide and the spinel occupy substantially the same space. 7.The catalytic converter according to claim 5, wherein the layered oxideand the spinel occupy partially overlapping regions.
 8. The catalyticconverter according to claim 1, wherein the layered oxide comprisesLaBaCoO₄.
 9. The catalytic converter according to claim 1, wherein thelayered oxide comprises LaBaFeO₄.
 10. The catalytic converter accordingto claim 1, wherein the layered oxide is in a nanoparticle form, of 2 to50 nm in diameter.
 11. The catalytic converter according to claim 1,wherein the spinel has a formula, Ni_(0.15)Co_(0.85)CoAlO₄.
 12. Thecatalytic converter according to claim 1, wherein the spinel is innanoparticle form, of 2 to 50 nm in diameter.
 13. A two-stage method forthe removal of NO_(x) from an exhaust gas stream, the method comprising:flowing the exhaust gas stream through a co-catalyst system comprising:exposing the exhaust gas stream to a layered oxide and catalyzing areduction of at least one of NO and NO₂ to generate N₂O; and contactingthe exhaust gas stream with a spinel having a formulaNi_(y)Co_(1-y)CoAlO₄, wherein y is a value within a range of about 0.1to about 0.9, inclusive, to decompose the N₂O to N₂.
 14. The method asrecited in claim 13, wherein the layered oxide has a formulaLa_(2-x)M_(x)QO₄, wherein: M is a cationic metal selected from the groupconsisting of: Ca, Sr, Ba, and a combination thereof; Q is a cationicmetal selected from the group consisting of: Fe, Ni, Co, and acombination thereof; and x is within a range of from about 0.01 to about1.5, inclusive.
 15. The method as recited in claim 13, wherein thelayered oxide comprises at least on of LaBaFeO₄ LaBaCoO₄.
 16. The methodas recited in claim 13, comprising exposing the exhaust gas stream tothe layered oxide prior to exposing the exhaust gas stream to thespinel.
 17. The method as recited in claim 13, comprising exposing theexhaust gas stream to the layered oxide and the spinel simultaneously.18. The method as recited in claim 13, comprising flowing the exhaustgas stream through the co-catalyst at a temperature less than about 500°C.
 19. The method as recited in claim 13, comprising recirculating theexhaust gas stream through the co-catalyst system.
 20. A catalyticconverter for the removal of NO_(x) from an exhaust gas stream operatingbetween 350 and 550° C., the catalytic converter comprising: an inletconfigured to receive the exhaust gas stream into an enclosure; anoutlet configured to allow the exhaust gas stream to exit the enclosure;and a co-catalyst system contained inside the enclosure, the co-catalystsystem having: a layered oxide having a formula La_(2-x)M_(x)QO₄, forcatalyzing a reduction reaction of at least one of NO and NO₂ togenerate N₂O, wherein: M is a cationic metal selected from the groupconsisting of: Ca, Sr, Ba, and a combination thereof; Q is a cationicmetal selected from the group consisting of: Fe, Ni, Co, and acombination thereof; and x is within a range of from about 0.01 to about1.5, inclusive; and a spinel having a formula, Ni_(y)Co_(1-y)CoAlO₄,wherein y is a value within a range of about 0.1 to about 0.9,inclusive, for catalyzing a decomposition reaction of N₂O to N₂.